Conventional lithographic printing techniques cannot accommodate true high-speed variable data printing processes in which images to be printed change from impression to impression, for example, as enabled by digital printing systems. The lithography process is often relied upon, however, because it provides very high quality printing due to the quality and color gamut of the inks used. Lithographic inks are also less expensive than other inks, toners, and many other types of printing or marking materials.
Ink-based digital printing uses a variable data lithography printing system, or digital offset printing system. A “variable data lithography system” is a system that is configured for lithographic printing using lithographic inks and based on digital image data, which may be variable from one image to the next. “Variable data lithography printing,” or “digital ink-based printing,” or “digital offset printing” is lithographic printing of variable image data for producing images on a substrate that are changeable with each subsequent rendering of an image on the substrate in an image forming process.
For example, a digital offset printing process may include transferring radiation-curable ink onto a portion of a fluorosilicone-containing imaging member surface that has been selectively coated with a dampening fluid layer according to variable image data. The ink is then cured and transferred from the printing plate to a substrate such as paper, plastic, or metal on which an image is being printed. The same portion of the imaging plate may be cleaned and used to make a succeeding image that is different than the preceding image, based on the variable image data. Ink-based digital printing systems are variable data lithography systems configured for digital lithographic printing that may include an imaging member having a reimageable surface layer, such as a silicone-containing surface layer.
Systems may include a dampening fluid metering system for applying dampening fluid to the reimageable surface layer, and an imaging system for laser-patterning the layer of dampening fluid according to image data. The dampening fluid layer is patterned by the imaging system to form a dampening fluid pattern on a surface of the imaging member based on variable data. The imaging member is then inked to form an ink image based on the dampening fluid pattern. The ink image may be partially cured, and is transferred to a printable medium, and the imaged surface of the imaging member from which the ink image is transferred is cleaned for forming a further image that may be different than the initial image, or based on different image data than the image data used to form the first image. Such systems are disclosed in U.S. patent application Ser. No. 13/095,714 (“714 application”), titled “Variable Data Lithography System,” filed on Apr. 27, 2011, by Stowe et al., which is commonly assigned, and the disclosure of which is hereby incorporated by reference herein in its entirety.
Systems have also been provided that obviate the expense attached to manufacturing suitable plates for some ink-based digital printing systems. For example, Dalal disclosed a system using solid ink jet to create an imaging plate for ink based digital printing in commonly-assigned U.S. application Ser. No. 13/529,581, titled “Method and Apparatus for Generating a Printing Member,” filed Jun. 21, 2012, the disclosure of which is hereby incorporated herein by reference in its entirety. A method of lithographic plate production is disclosed, wherein the image-wise hydrophobic and hydrophilic areas are created on the plate by inkjet. The lithographic plate contains areas of polymer, which results from hardening of the inkjet liquid, and areas of bare plate where the liquid was not applied. The bare plate is hydrophilic, and the polymer is designed to be hydrophobic, similar to the (exposed) photopolymer of the conventional process. In effect, the hydrophobic polymer is applied directly to the image areas using inkjet technology, instead of applying the hydrophobic polymer to the entire plate, imaging through film or laser, and removing the hydrophobic polymer from the non-image areas. Systems for enhanced ink-based digital printing are desired for high-speed, high image-quality printing.